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Consumer products such as clothing and medical products are increasingly integrating silver and silver nanoparticles (AgNPs) into base materials to serve as an antimicrobial agent. Thus, it is critical to assess the effects of AgNPs on wastewater microorganisms essential to biological nutrient removal. In the present study, pulse and continuous additions of 0.2 and 2 ppm gum arabic and citrate coated AgNPs as well as Ag as AgNO3 were fed into sequencing batch reactors (SBRs) inoculated with nitrifying sludge. Treatment efficiency (chemical oxygen demand (COD) and ammonia removal), Ag dissolution measurements, and 16S rRNA bacterial community analyses (terminal restriction fragment length polymorphism, T-RFLP) were performed to evaluate the response of the SBRs to Ag addition. Results suggest that the AgNPs may have been precipitating in the SBRs. While COD and ammonia removal decreased by as much as 30% or greater directly after spikes, SBRs were able to recover within 24 h (3 hydraulic retention times (HRTs)) and resume removal near 95%. T-RFLP results indicate Ag spiked SBRs were similar in a 16s rRNA bacterial community. The results shown in this study indicate that wastewater treatment could be impacted by Ag and AgNPs in the short term but the amount of treatment disruption will depend on the magnitude of influent Ag.

Ag Analytical Methods. Briefly, samples were diluted in an acid solution to digest stabilizing coatings and other compounds that could interfere with ICP-MS measurements. An Agilent 7700 inductively coupled plasma mass spectrometer (ICP-MS, Santa Clara, CA) was used to measure total and dissolved Ag. First, total Ag was measured by dissolving a sample of wastewater in 2% HNO 3 and 0.5% HCl concentrated acid for at least 24 h. Samples were separately taken to measure the amount of dissolved Ag in the wastewater. Dissolved Ag samples were defined as the fraction of Ag filtrate that can be passed through and Amicon® Ultra-4 Centrifugal Filter Unit (Millipore, Billerica, MA) and centrifuged at 7,000 rpm for 35 min. The filtrate was then acidified with nitric and hydrochloric acid using a method amended from Wang et al. 1 . DNA extraction and PCR Conditions. Biomass samples were taken periodically from the SBRs and micro-centrifuged for 1 min at 13,000 x g. Biomass samples were then immediately stored at -20°C until DNA extraction. Duplicate samples were extracted for

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